1. Field of the Invention
The present invention relates to a programmable semiconductor device including universal logic modules.
2. Description of the Related Art
In a programmable semiconductor device such as a field programmable gate array (FPGA) device, a logic cell formed by a plurality of kinds of universal logic modules is provided. Then, the user performs a connection operation upon the logic cell to realize a desired user logic circuit.
In a prior art programmable semiconductor device (see: JP-A-2002-198801), a logic cell is constructed by first universal logic modules serving as two-input, one-output multiplexers, second universal logic modules serving as inverters and a third universal logic module serving as a two-input, one-output multiplexer. Note that the third universal logic module has the same configuration as the universal logic modules except that an inverter having a large current driving ability is provided. Also, various kinds of user logic circuits can be made by the user using the first universal logic modules. This will be explained later in detail.
In order to cope with as many user inverters as possible in the logic cell of the above-described prior art programmable semiconductor device, the number of second universal logic modules may be increased. In this case, however, if the ratio of the first universal logic modules, the second universal logic modules and the third universal logic modules is inappropriate due to the increased number of the second universal logic modules, the number of unused logic modules may be increased, which would increase a wasted area of the logic cell.
Further, in the logic cell of the above-described prior art programmable semiconductor device, a user delay circuit can be realized by connecting a plurality of the second universal logic modules in series. In this case, however, long connections are required between the series of the second universal logic modules, so that a delay time of the user delay circuit is increased.
Still further, since all the second universal logic modules are of the same type, a realized user inverter has the same driving power and the same delay time. As a result, various kinds of user inverters cannot be realized.